Batten that are ready to go in a sail are classified by:
"Full battens are classified by their draft position and bend characteristics. The draft position is the fore and aft location of the maximum amount of bend at a given bend pressure. This measurement is given in a percentage of the batten's overall length, starting at the inboard end. The poundage it takes to reach this maximum draft position is the weight of the batten. For example, a batten would be classified as 56 inches long x 5/8 inches wide x 40% draft x 6.5 lbs." (from Ullman)

Blank stock is frequently classified by how many pounds hung from the middle of the batten it takes to deflect the center of a 40 inch batten tbd inches.

A sailor has different approuch. All he knows he needs a stiffer batten or softer batten and he just needs a way of comparing the battens he has. A sailor comparing battens, puts one end of the batten against the wall, connects a fish scale to the other end of the batten, then by pulling on the fish scale the sailor moves his end of the batten about 1/8 the total length of the batten closer to the end of the batten against the wall, and reads the scale. All you need is a fish scale and a tape measure to compare battens.